The present invention provides an improved blood leak detector to sense a rupture or other failure of a blood filter. A blood filter, for example, removes liquid from blood so that concentrated blood can be returned to the circulatory system of a patient. The filter has a blood passage and a filtrate passage that are separated by a filter membrane. The filter membrane allows some liquid to pass, but blocks large solutes and hemoglobin. Hemoglobin, large solutes and a substantial portion of the blood liquid flow through the blood passage of the filter, without passing through the filter membrane. However, if the filter membrane ruptures, hemoglobin and other blood cells and large solutes will flow through the membrane into the liquid filtrate flow. A rupture in the filter membrane can result in loss of desirable hemoglobin and blood cells from the blood being returned to the patient. A rupture in a blood filter should be detected to avoid loss of these blood cells and desirable solutes.
Blood leak detectors are used to detect a rupture in the membrane of a filter by sensing hemoglobin in the filtrate line of the filter. Blood leak detectors rely on the optical sensing of light passing through the blood filtrate tube. A decrease in the amount of light passing through the filtrate tube indicates the presence of hemoglobin in the filtrate and hence a ruptured filter membrane. However, prior blood leak detectors have several shortcomings including: their electronics are prone to drift and require frequent calibration; they are affected by ambient light and require clumsy shrouds to block ambient light from the sensor; they do not detect the absence of a filtrate tube or the absence of a cuvette; they respond differently to oxygenated and unoxygenated hemoglobin; they are difficult to operate and clean, and they tend to be expensive.